-Pre V2R5, the optimizer would have joined all 500 million rows of the TblA to all 100 million rows of TblB before grouping resulting
spool on TblA.Part_No (while summing Vol_Sold and Available_Qty)

-With V2R5, the optimizer will first group TblA on Part_No (while summing Vol_Sold) in parallel (?) with grouping TblB on Part_No (while
summing Available_Qty). Once complete, the optimizer will then join the resulting 2 spool files together via Part_No

Pre-V2R5, the optimizer would have joined TblA to TblC on Part_No prior to grouping data by TblC.Part_No and summing TblA.Vol_Sold With
V2R5, the optimizer first groups TblA on Part_No while summing Vol_Sold, then joins the resulting spool file to TblC on Part_No